My smallmouth bass has this weird pink/red spot at the base of his pectoral fin and I'm not sure why

[thebiggerthebetter]

I fail to see anything abnormal at the base of the pectoral fin.

 

[Kelly_Aquatics]

It looks stressed to me. I would put it in a quarantine tank or divide that tank so that is by itself and then up water changes to 2x a week. I don’t think it’s parasites; it doesn’t look emaciated

 

[Snap]

I agree with Americancichlidsaredabest and F FJB . You may have to isolate the smaller bass possibility it may get badly harmed
by larger one.
Also your aquarium may not be fully cycled because Nitrate is 0ppm.
Shake those test bottles for Nitrate well.

The tank was going 2-3 days after a water change I wouldn't assume it's enough time for it to cycle

 

[Snap]

I fail to see anything abnormal at the base of the pectoral fin.

Yeah I'm sorry it's hard to see I cant get good pictures because it's such a small fish

What about the ammonia and nitrite?

I forget the numbers right now but when I checked it, it was fine the numbers weren't anything bad